In a conventional electronic apparatus having an imaging function, such as a digital still camera or a digital video camera, a solid-state imaging device like a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) image sensor is used. A solid-state imaging device has pixels each including a combination of a photodiode that performs photoelectric conversion and transistors, and an image is formed based on pixel signals that are output from the pixels arranged in a two-dimensional fashion.
In a solid-state imaging device, for example, charge accumulated in a photodiode is transferred to an FD (Floating Diffusion) unit that has a predetermined capacity and is provided at the connecting unit between the photodiode and the gate electrode of an amplifying transistor. A signal at the level corresponding to the charge stored in the FD unit is read from the pixel, and is subjected to AD conversion at an AD (Analog Digital) conversion circuit having a comparator. The resultant signal is then output.
In recent years, there has been a demand for a decrease in the charge capacity of each FD unit and an increase in the conversion efficiency of each pixel device, so as to increase the sensitivity characteristics of a solid-state imaging device and obtain low-illuminance characteristics similar to those of an ultrasensitive image sensor.
For example, Patent Document 1 discloses a technology by which only the element separation regions in contact with FD units have trench structures, and the other element separation regions are formed with diffusion element separation regions, so as to cope with the small-sized pixels of MOS image sensors, and increase conversion efficiency while preventing generation of dark current and appearance of white dots.